Habitat destruction
Habitat destruction (also termed habitat loss and habitat reduction) occurs when a natural habitat is no longer able to support its native species. The organisms once living there have either moved to elsewhere or are dead, leading to a decrease in biodiversity and species numbers.[1][2] Habitat destruction is in fact the leading cause of biodiversity loss and species extinction worldwide.[3]
Humans contribute to habitat destruction through the use of natural resources, agriculture, industrial production and urbanization (urban sprawl). Other activities include mining, logging and trawling. Environmental factors can contribute to habitat destruction more indirectly. Geological processes, climate change,[2] introduction of invasive species, ecosystem nutrient depletion, water and noise pollution are some examples. Loss of habitat can be preceded by an initial habitat fragmentation. Fragmentation and loss of habitat have become one of the most important topics of research in ecology as they are major threats to the survival of endangered species.[4]
Impacts[edit]
On animals and plants[edit]
When a habitat is destroyed, the carrying capacity for indigenous plants, animals, and other organisms is reduced so that populations decline, sometimes up to the level of extinction.[39]
Habitat loss is perhaps the greatest threat to organisms and biodiversity.[40] Temple (1986) found that 82% of endangered bird species were significantly threatened by habitat loss. Most amphibian species are also threatened by native habitat loss,[41] and some species are now only breeding in modified habitat.[42] Endemic organisms with limited ranges are most affected by habitat destruction, mainly because these organisms are not found anywhere else in the world, and thus have less chance of recovering. Many endemic organisms have very specific requirements for their survival that can only be found within a certain ecosystem, resulting in their extinction. Extinction may also take place very long after the destruction of habitat, a phenomenon known as extinction debt. Habitat destruction can also decrease the range of certain organism populations. This can result in the reduction of genetic diversity and perhaps the production of infertile youths, as these organisms would have a higher possibility of mating with related organisms within their population, or different species. One of the most famous examples is the impact upon China's giant panda, once found in many areas of Sichuan. Now it is only found in fragmented and isolated regions in the southwest of the country, as a result of widespread deforestation in the 20th century.[43]
As habitat destruction of an area occurs, the species diversity offsets from a combination of habitat generalists and specialists to a population primarily consisting of generalist species.[3] Invasive species are frequently generalists that are able to survive in much more diverse habitats.[44] Habitat destruction leading to climate change offsets the balance of species keeping up with the extinction threshold leading to a higher likelihood of extinction.[45]
Habitat loss is one of the main environmental causes of the decline of biodiversity on local, regional, and global scales. Many believe that habitat fragmentation is also a threat to biodiversity however some believe that it is secondary to habitat loss.[46] The reduction of the amount of habitat available results in specific landscapes that are made of isolated patches of suitable habitat throughout a hostile environment/matrix. This process is generally due to pure habitat loss as well as fragmentation effects. Pure habitat loss refers to changes occurring in the composition of the landscape that causes a decrease in individuals. Fragmentation effects refer to an addition of effects occurring due to the habitat changes.[4] Habitat loss can result in negative effects on the dynamic of species richness. The order Hymenoptera is a diverse group of plant pollinators who are highly susceptible to the negative effects of habitat loss, this could result in a domino effect between the plant-pollinator interactions leading to major conservation implications within this group.[47] It is observed from the worlds longest running fragmentation experiment over 35 years that habitat fragmentation has caused a decrease in biodiversity from 13% to 75%. [48]
Outlook[edit]
The rapid expansion of the global human population is increasing the world's food requirement substantially. Simple logic dictates that more people will require more food. In fact, as the world's population increases dramatically, agricultural output will need to increase by at least 50%, over the next 30 years.[56] In the past, continually moving to new land and soils provided a boost in food production to meet the global food demand. That easy fix will no longer be available, however, as more than 98% of all land suitable for agriculture is already in use or degraded beyond repair.[57]
The impending global food crisis will be a major source of habitat destruction. Commercial farmers are going to become desperate to produce more food from the same amount of land, so they will use more fertilizers and show less concern for the environment to meet the market demand. Others will seek out new land or will convert other land-uses to agriculture. Agricultural intensification will become widespread at the cost of the environment and its inhabitants. Species will be pushed out of their habitat either directly by habitat destruction or indirectly by fragmentation, degradation, or pollution. Any efforts to protect the world's remaining natural habitat and biodiversity will compete directly with humans' growing demand for natural resources, especially new agricultural lands.[56]